The present invention relates generally to titanium braze foils and more particularly to titanium braze foils with zirconium.
Braze alloys based on titanium (Ti) are useful for braze components that consist of titanium, nickel (Ni) and/or iron/steel (Fe) based elements or alloys, among other uses. Thin gauge braze sheets or foils have proven useful for preplacing filler metal in braze joints and/or for bonding to base metal materials to form a clad base-metal structure that has its own braze filler on the surface. The lower melting points of common Ti-based braze alloys cause a beneficial minimum effect on the microstructures and mechanical properties of the brazed components. Furthermore, Ti-based braze alloys tend to provide corrosion resistance that is superior to conventional copper (Cu) or silver (Ag) based braze alloys.
Ti alloys undergo microstructural changes when they are processed above their beta transus. The beta transus of Ti alloys refers to the temperature at which Ti undergoes a complete phase transformation from an alpha plus beta microstructure to an all beta structure or vice versa and results in crystal structure changes. Those microstructural changes can be harmful to the material properties, causing grain growth, reduced fatigue resistance and reduced ductility. Additionally, during brazing the molten braze filler reacts with the parent metal, dissolving it and diffusing into it, which can cause unwanted changes in the parent metal and brazed joint properties. The brazing temperature has to be kept as low as possible and holding time has to be minimized as well to avoid the aforementioned changes in the properties and structure of the part being brazed.
The addition of Zr to the Ti—Cu—Ni braze alloy allows melting (brazing) to occur at lower temperatures than does a Ti—Cu—Ni braze alloy without Zr. The lowered brazing temperature results in reduced undesirable microstructure changes in the brazed parts after brazing. Reduced microstructure changes cause less embrittlement of the brazed parts. Because embrittlement is detrimental to the ductility and fatigue resistance of the brazed parts, the use of a Ti—Cu—Ni braze alloy with added Zr, and the concomitant lowered brazing temperature, may result in brazed materials with better mechanical properties than would otherwise be obtained using a Ti—Cu—Ni braze alloy without added Zr.
U.S. Pat. No. 6,149,051 discloses a braze alloy of 40Ti-20Zr-20Cu-20Ni in the form of a homogenous mixed powder braze filler. While useful for smaller applications, powder braze fillers may present problems when brazing large sheet metal products. The filler must be uniformly coated onto the parent metal sheets which require special equipment.
U.S. Pat. No. 6,475,637 discloses a Ti—Ni—Cu braze foil comprising 10.5-12.5 wt % Zr which is formed by rapid solidification to produce a homogeneous thin foil. The rapid solidified foil is limited in the width, length and quantity of the foil. Furthermore, the manufacture of the braze foil by rapid solidification can be relatively expensive.
As can be seen, there is a need for braze foils and sheets made of an alloy of Ti, Zr and other metals that would have a low melting point and be useful for brazing large sheet metal products. It would also be desirable if such braze foils and sheets could be manufactured easily and inexpensively.